Combustible materials and the threat of fire caused panic in large metropolitan cities

In the early 1900’s the use of combustible materials and the threat of fire caused panic in large metropolitan cities. During the 1980’s, it was common place to train children in schools to seek shelter in the event of a nuclear attack. Many buildings (perhaps some schools you have been in) have had bomb shelters built in basements. Today, the perceived threat to school age children is greatest from an active shooter / terrorist event. What framework was used to get us from from those early points of the 1900’s to today. Can you name some of the systems or organizations that were integrated to form the current emergency management model we use today?